<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Title</title>
</head>
<body>
<script>
  // hasOwnProperty() : 看是不是对象自身下面的属性
  let arr = [];
  arr.num = 10;
  Array.prototype.num2 = 20;
  console.log(arr.hasOwnProperty("num"));
  console.log(arr.hasOwnProperty("num2"));
</script>
</body>
</html>
